Photopatternable molecular circuitry

ABSTRACT

Bistable molecules are provided with at least one photosensitive functional group. As thus constituted, the bistable molecules are photopatternable, thereby allowing fabrication of micrometer-scale and nanometer-scale circuits in discrete areas without relying on a top conductor as a mask. The bistable molecules may comprise molecules that undergo redox reactions, such as rotaxanes and catenanes, or may comprise molecules that undergo an electric-field-induced band gap change that causes the molecules, or a portion thereof, to rotate, bend, twist, or otherwise change from a substantially fully conjugated state to a less conjugated state. The change in states in the latter case results in a change in electrical conductivity.

TECHNICAL FIELD

The present invention relates generally to methods of making electroniccircuitry, and, more particularly, to forming the elements of theelectronic circuitry directly, without the need for separate photoresiststeps.

BACKGROUND ART

Photoresist masks for patterning layers to fabricate electronic circuitsare well-known. That technology is the basis for today's microcircuits.Briefly, positive or negative polymeric resists are used, involving theformation of a layer of resist on a surface, exposing the resist toradiation (visible, UV, X-ray, etc.) through a mask to cross-link (orunlink) portions of the resist, followed by removal of unwanted portionsof the resist. The resist then serves as a mask for further processingsteps, such as ion implantation, oxidation, metallization, and the like.

The area of molecular electronics is in its infancy. Developments innanotechnology (critical dimension measured in nanometers) are directedto new generations of electronic circuitry, having much smallerdimensions than present technology can provide.

While a number of different approaches have been developed, one that isof current interest involves self-assembled wires, with at least oneconnector species between connecting pairs of wires to form a junction.The connector species comprises a bistable molecular switch. Suchswitches can be configured as, for example, crossbar memories and logiccircuits. The investigations are reported, for example, by C. P. Collieret al., Science, Vol. 285, pp. 391–394 (16 Jul. 1999) and C. P. Collieret al., Science, Vol. 289, pp. 1172–1175 (18 Aug. 2000); see also U.S.Pat. No. 6,128,214, entitled “Molecular Wire Crossbar Memory”, issuedOct. 3, 2000, to P. J. Kuekes et al and U.S. Pat. No. 6,256,767,entitled “Demultiplexer for a Molecular Wire Crossbar Network (MWCNDEMUX)”, issued to P. J. Kuekes et al on Jul. 3, 2001.

The references in the foregoing paragraph deal with oxidation/reduction(“redox”) reactions involving, for example, rotaxanes, pseudo-rotaxanes,catenanes, and spiropyrans as the connector species. More recent workhas shown that the connector species may comprise molecules thatevidence an electric-field induced band gap change as a consequence ofsome mechanical action; see, e.g., application Ser. No. 09/823,195,filed Mar. 29, 2001, entitled “Bistable Molecular Mechanical Deviceswith a Band Gap Change Activated by an Electric Field for ElectronicSwitching, Gating, and Memory Applications”, and assigned to the sameassignee as the present application. The molecular system employed asthe connector species has an electric-field induced band gap change, andthus a change in its electrical conductivity, that occurs via one of thefollowing mechanisms: (1) molecular conformation change (e.g., rotationof a part of the molecule with respect to another part of the molecule);(2) change of extended conjugation via chemical bonding change to alterthe band gap (e.g., charge separation or recombination of the molecule);or (3) molecular folding or stretching. Nanometer-scale reversibleelectronic switches are thus provided that can be assembled easily tomake cross-bar circuits, which provide memory, logic, and communicationfunctions.

The patterning of nano-scale circuits with conventional photoresistspresents a daunting task, and requires novel methods. Making and usingresist by conventional means (especially in direct contact with themolecule, or connector species) could adversely alter the properties ofthe ultra-thin junction. Further, barrier materials between the moleculeand the conventional resist could adversely alter the properties of thejunction itself; for example, many metallic species could diffuse intoor bind tightly with the molecule, becoming essentiallyunremovable/inseparable.

Polymer electronics on this thickness scale (nanometers) presentsspecial problems (rotaxane studies by Collier et al, supra, are on theorder of 100 Å or less). The present invention sidesteps the use ofimprinting techniques and makes intermediate mask transfer unnecessary.The present invention is useful in both micrometer-scale andnanometer-scale devices.

DISCLOSURE OF INVENTION

In accordance with the present invention, bistable molecules areprovided with at least one photosensitive (ultraviolet, electron-beam,or X-ray) functional group. As thus constituted, the bistable moleculesare photo-patternable, thereby allowing fabrication of circuits. Thebistable molecules may comprise molecules that undergo redox reactions,such as rotaxanes and catenanes, or, more preferably, may comprisemolecules that undergo an electric-field induced band gap change thatcauses the molecules, or a portion thereof, to rotate, bend, twist, orotherwise change from a substantially fully conjugated state to a lessconjugated state. The change in states in the latter case results in achange in electrical conductivity.

Specifically, a bistable molecule for a multiple electrode devicecomprises at least one pair of electrodes that form at least onejunction and at least one connector species connecting the pair ofelectrodes in the junction, where the junction has a functionaldimension in nanometers or micrometers. The connector species comprisesthe bistable molecule provided with at least one photosensitivefunctional group for patterning the connector species.

Also in accordance with the present invention, a method is provided forfabricating the multiple electrode device. The method comprises:

-   -   (a) forming a first set of the electrodes on a substrate;    -   (b) depositing a film of the bistable molecule, including the        photosensitive group, on the electrodes;    -   (c) exposing portions of the bistable molecular film to        irradiation (ultraviolet, electron-beam, or X-ray); and    -   (d) removing unwanted portions of the bistable molecular film to        provide a photo-patterned molecular film.

A second set of the electrodes may be deposited adjacent the first setof the electrodes, either above (at a non-zero angle thereto) or in thesame plane as the first set of electrodes. Alternatively, the second setof electrodes may be eliminated if the resulting device is probe-tipaddressable.

Multiple sheets of molecules may be employed in the practice of thepresent invention. Alternatively, multiple discrete islands of differentmolecules may be employed.

An advantage of the present invention over the prior art is that the topelectrode (the second set of electrodes) does not define the junction.Rather, the molecular area is defined independently, due to the use ofthe photosensitive group.

The present invention provides a class of bistable molecular switcheswith at least one photosensitive functional group on the molecule. Thosemolecules can serve as both a molecular device and photoresist-type maskfor patterning a layer to fabricate molecular circuits. This willsimplify the traditional process and shorten the time to produce a batchof circuits, leading to inexpensive products, such as electronic memory(write once or rewriteable), electronically addressable displays, andgenerally any circuit for which organic electronics or opto-electronicswill be acceptable.

Advantageously, the present invention reduces or eliminates conventionalphotoresist masking layers, and simplifies the fabrication ofmicro-scale and nano-scale circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective elevational view, schematically depicting twocrossed wires, with at least one molecule at the intersection of the twowires;

FIGS. 2 a–2 f provide a schematic representation of the prior art stepsthat use lithographically deposited (micrometer or sub-micrometer scalediameter) wires;

FIGS. 3 a–3 d depict a schematic representation of process steps inaccordance with the present invention for producing photo-patternablemolecular circuitry;

FIG. 4 is a schematic representation of a two-dimensional array ofswitches, depicting a 4×3 crossbar switch, wherein the switching isvertical;

FIG. 5 is a schematic representation of an array of individual switcheswherein the switching is horizontal;

FIG. 6 is a schematic representation of one generic embodiment of thepresent invention, illustrating the breaking of a chemical bond betweena main molecular switching unit and an attaching group due tophotochemical decomposition;

FIG. 7 is a schematic representation of another generic embodiment ofthe present invention, illustrating the transformation of a mainmolecular switching group from insolvable to solvable in solvents due tophotochemical transformation; and

FIG. 8 is a schematic representation of yet another generic embodimentof the present invention, illustrating the transformation of a mainmolecular switching group from solvable to insolvable in solvents due tophotochemical transformation.

BEST MODES FOR CARRYING OUT THE INVENTION

Definitions

As used herein, the term “self-aligned” as applied to “junction” meansthat the junction that forms the switch and/or other electricalconnection between two wires is created wherever two wires, either ofwhich may be coated, cross each other, because it is the act of crossingthat creates the junction. The junction in its critical dimensions maybe measured in nanometers or micrometers.

The term “self-assembled” as used herein refers to a system thatnaturally adopts some geometric pattern because of the identity of thecomponents of the system; the system achieves at least a local minimumin its energy by adopting this configuration.

The term “singly configurable” means that a switch can change its stateonly once via an irreversible process such as an oxidation or reductionreaction; such a switch can be the basis of a programmable read-onlymemory (PROM), for example.

The term “reconfigurable” means that a switch can change its statemultiple times via a reversible process such as an oxidation orreduction; in other words, the switch can be opened and closed multipletimes, such as the memory bits in a random access memory (RAM).

The term “bistable” as applied to a molecule means a molecule having tworelatively low energy states. The molecule may be either irreversiblyswitched from one state to the other (singly configurable) or reversiblyswitched from one state to the other (reconfigurable).

The term “micron-scale dimensions” refers to dimensions that range from1 micrometer to a few micrometers in size.

The term “sub-micron scale dimensions” refers to dimensions that rangefrom 1 micrometer down to 0.04 micrometers.

The term “nanometer scale dimensions” refers to dimensions that rangefrom 0.1 nanometers to 50 nanometers (0.05 micrometers).

The terms “micron-scale wires” and “submicron-scale wires” generallyrefer to rod or ribbon-shaped conductors or semiconductors with widthsor diameters having the dimensions of 0.1 to several micrometers, andheights that can range from a few tens of nanometers to severalmicrometers.

“HOMO” is the common chemical acronym for “highest occupied molecularorbital”, while “LUMO” is the common chemical acronym for “lowestunoccupied molecular orbital”. HOMOs and LUMOs are responsible forelectronic conduction in molecules.

Crossed Wire Switch

There are many possible configurations for fabricating nanometer-scaleand micrometer-scale devices. One such approach employs crossed-wireswitches. Another approach involves probe-addressable devices. Thepresent invention is not limited to the particular configuration of thedevice, but rather is directed to photopatterning the molecular speciesemployed in the device. Because the field of molecular electronics isstill relatively new, a crossed-wire switch is described below.

The essential device features are disclosed in co-pending patentapplication Ser. No. 09/280,048, filed Mar. 29, 1999, incorporatedherein by reference and shown in FIGS. 1 a–1 b. A crossed wire switch 10comprises two wires 12, 14, each either a metal or semiconductor wire,that are crossed at some non-zero angle. In between those wires is alayer of molecules or molecular compounds 16, denoted R in FIGS. 1 a and1 b. The particular molecules 18 (denoted R_(S)) that are sandwiched atthe intersection of the two wires 12, 14 are identified as switchmolecules and exist at a junction defined by the two wires. When anappropriate voltage is applied across the wires, the switch moleculesare either oxidized or reduced. When a molecule is oxidized (reduced),then a second species is reduced (oxidized) so that charge is balanced.These two species are then called a redox pair. One example of thisdevice would have a molecule undergo reduction, and then a secondmolecule (the other half of the redox pair) would be oxidized. Inanother example, a molecule is reduced, and one of the wires isoxidized. In a third example, a molecule is oxidized, and one of thewires is reduced. In a fourth example, one wire is oxidized, and anoxide associated with the other wire is reduced. See also U.S. Pat. No.6,128,214, entitled “Molecular Wire Crossbar Memory”, issued to P. J.Kuekes et al on Oct. 3, 2000, and U.S. Pat. No. 6,256,767, entitled“Demultiplexer for a Molecular Wire Crossbar Network (MWCN DEMUX)”,issued to P. J. Kuekes et al on Jul. 3, 2001, both of which areincorporated herein by reference.

Depending on the molecules or materials that are used between the wires(the electrodes), each junction can either display the types ofelectrical function described below immediately on contact of the wiresor the junction can have a switching function that acts to connect ordisconnect the two wires together electrically. This switch can beeither singly configurable or reconfigurable. In the first case, theinitial state of the switch is open or closed. Electrically biasing theswitch beyond a particular threshold voltage that is determined by thematerials in the junction, which is essentially an electrochemical cell,oxidizes or reduces the material or molecules between the wires toirreversibly close or open the switch, respectively, thus permanentlyreversing its initial state. In the second case, by cycling the polarityand magnitude of the voltage on the switch beyond the appropriatethreshold values, it is possible to reversibly oxidize or reduce theproperly selected materials or molecules to close or open the switchmany times. In either case, when closed, the type of electricalconnection that is made between the wires depends upon the materialsfrom which the wires (or electrodes) are fabricated as well as theidentity of the molecules or materials between the wires.

Further, FIG. 1 depicts a coating 20 on wire 12 and a coating 22 on wire14. The coatings 20, 22 may be modulation-doping coatings, tunnelingbarriers (e.g., oxides), or other nano-scale functionally suitablematerials. Alternatively, the wires 12, 14 themselves may be coated withone or more R species 16, and where the wires cross, R_(S), or junction,18 is formed.

Different functions can be obtained from various combinations ofelectrode materials and materials or molecules used in the junction. Forexample, a resistor has a linear current-voltage characteristic, and ismade by intentionally over-reducing the junction between various typesof wires to essentially form a short circuit between the wires. Theopposite of this process is to over-oxidize a junction, which willconsume the wire in a localized region and effectively break the wire(acting as a fuse and creating an open circuit) in that wire at theposition of the junction. A tunneling resistor maintains a thin,insulating barrier (approximately 2 nm thick) between wires and has anexponential current-voltage characteristic. In the case where junctionmolecules or materials have a sharply defined energy state which liesinside the band gap of an electrically insulating barrier that can beaccessed by electrically biasing the junction, the connection betweenthe wires can exhibit a flow of electrical current that is dominated bythe process of resonant tunneling. The resonant tunneling can produceone or more inflection points in the otherwise exponentialcurrent-voltage characteristic of a tunneling resistor.

A diode is a junction that passes current more easily in one directionthan in the other, and thus has an asymmetry in the current-voltagecharacteristic for positive and negative voltages. A tunneling diode hasboth the positive-negative voltage asymmetry of the diode and theexponential current-voltage characteristic of the tunneling resistor. Aresonant tunneling diode has a positive-negative voltage asymmetry aswell as a peak in its current-voltage characteristic, such that over arestricted range of increasing voltage magnitude the current magnitudeactually decreases, a phenomenon that is known as negative differentialresistivity.

Finally, a battery is a circuit element that acts to hold a constantvoltage difference between its electrodes as long as the battery issufficiently charged, e.g., there is a sufficient supply of oxidizingand reducing agents separated by an insulating barrier. Charging thebattery is accomplished by placing the appropriate voltage across thejunction, which as stated before is an electrochemical cell, to onlypartially oxidize or reduce the material or molecules in the junction.

In general, any real junction between wires formed by the processesdescribed above will actually have two or more of the electricalfunctions described, with the effective circuit elements connected inseries. Additionally, capacitors may be formed.

Thus, any number of metallic or semiconducting wire/moleculecombinations can be employed to provide useful devices, depending on thedevice properties desired from the assembled circuit. As describedabove, probe-tip addressable devices are also benefited in accordancewith the teachings herein.

Fabrication of Wire Electrodes

The above-identified co-pending application Ser. No. 09/280,048describes a number of processes to produce discrete crossed wire pairs,such as shown in FIG. 1. Also disclosed therein is a process forpreparing devices made from redox pairs of micrometer-scale wires.

Molecular switching components may come from any number of differentclasses of molecules, depending, again, on the desired properties of thedevice. The key requirement of the molecules is that, when they aresandwiched between two electrodes, they may be electrochemicallymodified (i.e., oxidized or reduced) by applying a voltage between theelectrodes. When the molecular components are so modified, the neteffect is that a barrier, e.g., a tunneling barrier, between the twowires is modified, and the rate of current flow is changed. This formsthe basis of a switch that can, in turn, be used for memory, logicoperations, and communication and signal routing networks. Molecularswitches can include redox pairs of molecules, in which application of avoltage reduces one of the molecules and oxidizes the other.

In the foregoing embodiment, the connector species 16 may comprise amaterial that displays a significant, or measurable, hysteresis in itscurrent-voltage curve, obtained from current-voltage characteristics ina solid-state junction. Examples of such species include metalocenes,rotaxanes, pseudo-rotaxanes, catenanes, and spiropyrans.

In another, more preferred, embodiment, the connector species maycomprise a material that evidences switching based on electric (E) fieldinduced band gap changes that have been discovered. These materials arethe subject of a copending patent application Ser. No. 09/823,195, filedon Mar. 29, 2001, entitled “Bistable Molecular Mechanical Devices with aBand Gap Change Activated by an Electric Field for Electronic Switching,Gating, and Memory Applications”, by Xiao-An Zhang et al. and assignedto the same assignee as the present application. Three primarymechanisms are disclosed and claimed; one of the mechanisms has twodifferent approaches. The mechanisms are:

-   -   (1) Electric field (“E-field”) induced rotation of at least one        rotatable section (rotor) of a molecule to change the band gap        of the molecule (rotor/stator configuration);    -   (2) E-field induced charge separation or recombination of the        molecule via chemical bonding change to change the band gap:        -   (2a) E-field-induced band gap change caused by the change of            extended conjugation via charge separation or recombination            accompanied by increasing or decreasing π- and/or p-electron            localization;        -   (2b) E-field-induced band gap change caused by change of            extended conjugation via charge separation or recombination            and π-bond breaking or formation; and    -   (3) E-field induced band gap change via molecular folding or        stretching.

The above-mentioned co-pending patent application Ser. No. 09/280,048discloses, inter alia, the preparation of micrometer-scale wires byshadow masking. Devices made from redox pairs could be preparedaccording to the method depicted in FIGS. 2 a–2 f. An insulatingsubstrate 24 (SiO₂, for example) is coated with a photosensitive resist26 and then covered with a photomask 28 and exposed to light 30, asillustrated in FIG. 2 a. The exposed pattern is developed, a resistpattern is formed (FIG. 2 b) and a metal layer 12 (Al, for example) isdeposited onto the substrate 24 (FIG. 2 c). A thin (1 to 2 nm)insulating layer 20 (Al₂O₃) is formed on the Al surface—in this case bysimple exposure of the patterned substrate to air, as shown in FIG. 2 c.Lift-off is used to form the metallic wire structure shown in FIG. 2 d.Next, a redox pair 16, labeled R in the Figure, is deposited either bychemically selective deposition onto the Al₂O₃, as a Langmuir film overthe entire substrate, or by sublimation of the molecules onto the entiresubstrate. In the latter case, redox pairs exist both on 16 a and off 16b the deposited wire 12 and its insulating layer 20, as shown in FIG. 2e. Next, a second wire 14 is deposited perpendicular to the first wire12 through a shadow mask, as shown in FIG. 2 f. The second wire 14 maybe comprised of one or more layers (the wire itself or a layer 32, Ti orCr, for example) which will form a interface with the depositedmolecules, followed by the thicker wire 14′ deposited on top of thebuffer layer, or it may just consist of wire 14. Only where the twowires 12, 14 cross (junction 18) is a device 10 defined, since anapplication of a voltage across the two wires is necessary to addressthe device. Thus, as long as the two wires 12, 14 intersect, no furtheralignment of the two lithographic steps is necessary in order to make asingle device 10.

While the foregoing process is useful for large micrometer-scaledevices, it would be difficult, if not impossible, to implement forsmall micrometer- and submicrometer-scale devices. In accordance withthe present invention, a photoresistless process is provided, whichsimplifies the processing, eliminates the need for photoresistdefinition of the top electrode (which would allow reduced mask featuresover a shadow mask), and eliminates the need for a top electrode todefine the junction. Further, the teachings of the present inventionprovide process alternatives without molecular degradation and makepossible other configurations, including, but not limited to, (1)multiple films, each in a discrete area, and (2) switches that operatelaterally, instead of vertically. That process is now described, withreference to FIGS. 3 a–3 d.

Present Invention

In addition to patterning the wires 12, 14, it is the connector species16 itself that is patterned. The junction 18 is no longer exclusivelydefined by patterning a top wire and allows multiple patterns, andpossibly multiple molecules, each in its own area (or stack) beforedeposition of the top electrode 14, if any. The process of the presentinvention also reduces cross-talk and capacitance to substrate.

FIG. 3 a depicts the formation of film 12 on a substrate 24. Film 12forms the bottom layer of wires. FIG. 3 a also depicts the deposition ofa layer of the connector species 16′ over the entire surface of the wirefilm 12. In FIG. 3 b, a patterned mask 28 is placed on top of theconnector species, and portions of the connector species 16′ are exposedby UV light 30 a, which passes through transparent regions 28′ in themask 28 to form a predetermined pattern in the connector layer 16′(regions 16′a protected by portions of the mask 28, regions 16′b exposedto UV). Alternatively, electron beam direct write procedures may beemployed, using electronic scanning of an e-beam to provide controlledexposure without a mask. Prior to deposition, the connector species 16′is modified, as discussed below, to incorporate one or morephotosensitive functional groups. FIG. 3 c depicts the resultantpatterned memory following development (patterned connector species16′a), prior to deposition of the top layer of wires 14 thereon, if any.FIG. 3 d depicts the final product. It differs from FIG. 2 f in that thedevice 10 of FIG. 3 d can be three orders of magnitude smaller than thatof FIG. 2 f and in that the connector species 16′a is independent of theintersection 18 between wires 12 and 14.

The process depicted in FIGS. 3 a–3 d is similar to the conventionalphotoresist process, but provides a film that has a thickness measuredin nanometers that is an active component in the circuit.

The key to realizing the benefits of the present invention involves themodification of a connector species 16 by adding to the connectorspecies a photosensitive chain, resulting in modified connector species16′. The presence of the photosensitive chain renders the connectorspecies sensitive to UV, electron beam, X-ray, etc. irradiation in theprocess depicted in FIGS. 3 a–3 d.

FIG. 4 depicts one implementation of vertical switching, namely, acrossbar switch 40, comprising a two-dimensional array of switches 10.FIG. 4 depicts a 4×3 array 40, but the invention is not limited to theparticular number of elements, or switches, 10, in the array. Access toa single point, e.g., 2 b, is accomplished by applying a voltage towires 2 and b to cause a change in the state of the molecular species 16at the junction 18 thereof, as described above. Details of the operationof the crossbar switch array 40 are further discussed inabove-referenced U.S. Pat. No. 6,128,214.

FIG. 5 depicts one implementation of horizontal switching, wherein theconnector species 16′a is disposed laterally between two electrodes 12and 14.

Turning now to a discussion of the modification of the molecular speciesemployed in the foregoing switches, the present invention providesmicrometer and nanometer-scale reversible optical and/or electronicswitches that can be assembled easily to make crossbar and othercircuits. The crossbar circuits have been described in the above-listedseries of patent applications and issued patents. The circuits providememory, logic and communications functions. One example of theelectronic switches is the so-called crossed-wire device, describedabove, wherein the connector species comprises the molecular systemdisclosed and claimed herein.

The present invention relies on one significant property: that thosephotopatternable molecular switches are essentially very stable withoutexposure to irradiation (UV, electron beam, or X-ray, etc.), wherein themolecular system undergoes photodecomposition upon exposure to theradiation, generating decomposition products that are easily removed.Thus, one can deposit a film of such a molecular system onto a substrateof some type, such as by self-assembly, chemical deposition, vapordeposition, or Langmuir-Blodgett deposition, etc.

The key to realizing the benefits of the present invention involves themodification of a connector and/or spacer species of the molecularsystem by adding to the connector and/or spacer species of the molecule,a photosensitive group (PSG). This photosensitive group disrupts themolecular system upon irradiation, creating the decomposition products.The attachment of a photosensitive group is preferably at one or bothend(s) of the molecular structure, near the point of the attachment tothe substrate. In addition, more PSG groups can be introduced into oneor more spacer species of the molecular system. The modified molecularsystem with at least one PSG built-in is either chemically bonded to thesubstrate (e.g., electrode, another molecular system, etc.) or via vander Waals' epitaxy. It is physically and/or chemically stable to certainsolvent(s) and cannot be simply removed by washing without being exposedto irradiation (UV, electron beam, or X-ray, etc.). But the PSG(s) ofthe molecular system undergo(es) a photochemical transformation ordecomposition upon irradiation. The photo-chemically-transformedmolecular system becomes very physically unstable and/or very soluble tocertain solvent(s) (e.g., aqueous acid, aqueous base, alcoholicsolvent(s), etc.) and can be easily removed by simple washing orextraction, etc.

The following requirements must be met in the modified molecular systemsof the present invention:

-   -   (a) The molecular system must be physically and/or chemically        stable without being exposed to irradiation (UV, electron beam,        or X-ray, etc.);    -   (b) The molecular system must be physically and/or chemically        unstable upon irradiation and can be easily removed by a simple        one time (or more times) solvent(s) extraction or washing;    -   (c) The photosensitive group (PSG) can be introduced either on a        side-arm (e.g., connecting and/or spacing unit(s), etc.) or on        the main body as part of the molecular switching system (e.g.,        azo, etc.);    -   (d) The photosensitive group introduced into the side-arm (e.g.,        connecting and/or spacing units) should not interfere with or        alter the electronic and/or optical properties of the molecular        switching system; ideally, it (or they) should be at least one        —CH₂— unit away from the main switching body;    -   (e) The photosensitive group can undergo either photochemical        decomposition or photochemical transformation, or a combination        of both;    -   (f) When the PSG is being introduced into a side-arm of the        molecular system, it must be a chemically-bonded connecting unit        between the main switching body and the attaching unit; it        severs the molecular main body (actual switching unit) from the        attaching unit by photochemical decomposition;    -   (g) When the PSG is being introduced into a side-arm of the        molecular system, it can undergo photochemical transformation to        change some physical and/or chemical properties of the        molecules, and make the transformed molecule become either        acidic, or basic, or more soluble in certain solvent(s) systems        (preferably, aqueous base, aqueous acid, alcohol or other common        organic solvent(s) systems);    -   (h) When the PSG severs the molecular main body (actual        switching unit) from the attaching unit by photochemical        decomposition, the remaining part of the attaching unit on the        substrate should not have any significant electrical and/or        optical properties to interfere with the functioning of the        molecular circuitry. The attaching unit can be, but is not        limited to, any one of following: S, O, B, N, P, Se,        hydrocarbon, or substituted hydrocarbon; and    -   (i) The PSG unit can be, but is not limited to, any one of        following: photosensitive azo, photosensitive ester or ether,        photosensitive amide or imide, photosensitive amine or imine,        photosensitive carbonate or carbamate, photosensitive thio-ether        or thio-ester, photosensitive isocyanides, photosensitive        hetero-ring system with at least one of hetero-atom (e.g., N, O,        S, B, P, etc.).

Following are some examples of PSG-modified molecular switching systems.Examples 1, 2 and 3 below show three different ways of constructing PSGsinto the molecular switching system and how the PSG works uponirradiation. This design allows different type of molecular films andelectrodes to be used, depending on the desired results.

Turning first to Example 1a, shown in FIG. 6, a first generic molecularexample is depicted for the present invention. Example 1b, whichfollows, depicts a specific molecular system.

FIG. 6 is a schematic representation of one generic embodiment of thepresent invention, illustrating the breaking of a chemical bond 60between a main molecular switching unit 62 and an attaching group 64 dueto photochemical decomposition. A photosensitive group 66 is initiallyinterposed between the main molecular switching unit 62 and theattaching group 64, which in turn is used to attach the main molecularswitching unit to an electrode, or other substrate, 68. With thepresence of the photosensitive group, the main molecular switching unit62 is fully bonded and cannot be physically removed via extraction orwashing. However, exposure of the molecule 70 to electromagneticradiation hν is sufficient to cause photochemical decomposition, therebybreaking the bond 60 between the main molecular switching unit 62 andthe attaching group 64. Consequently, the main molecular switching unitcan now be easily removed via extraction or washing. The attaching group64 does not interfere with the device.

In Example 1a, the attaching group 64 may be one of the following:carboxylic acid or its derivatives, sulfuric acid or its derivatives,phosphoric acid or its derivatives, hetero atoms (e.g., N, O, S, B, Se,P), or functional groups with at least one of above-mentioned heteroatoms, hydrocarbons or substituted hydrocarbons. The photosensitivegroup (PSG) 66 can be, but not limited to, any one of following:photosensitive azo, photosensitive ester or ether, photosensitive amideor imide, photosensitive amine or imine, photosensitive carbonate orcarbamate, photosensitive thio-ether or thio-ester, photosensitiveisocyanides, photosensitive hetero-ring system with at least one ofhetero-atom (e.g., N, O, S, B, P, etc.).

Without being exposed to irradiation, the molecular switching system 70is fully chemical bonded to the substrate (electrode, etc.) 68 throughthe PSG 66 and attaching group 64. It is stable and cannot be physicallyremoved by solvent extraction or washing. Once being exposed toirradiation (UV, electron beam, X-ray, etc.), the bonding between thesubstrate 68 and the main body of the system has been broken due to aphotochemical decomposition. The main body of the switching system(molecular system) can be removed easily from the surface of thesubstrate 68 by solvent extraction or washing.

Example 1b below is a real molecular example of one embodiment of thepresent invention, which relies on a rotor portion combined with astator portion. In Example 1b, the rotation axis of the rotor isdesigned to be in a 30 to 70 degree angle to the net current-carryingaxis of the molecules.

where:

The symbol A⁻ is an Acceptor group; it is an electron-withdrawing group.It may be one of following: carboxylic acid or its derivatives, sulfuricacid or its derivatives, phosphoric acid or its derivatives, nitro,nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br), functional groupwith at least one of above-mentioned hetero atoms (e.g., OH, SH, NH,etc.), hydrocarbons (either saturated or unsaturated), or substitutedhydrocarbons.

The symbol D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), substituted hydrocarbon,or a functional group with at least one of hetero atom (e.g., B, Si, I,N, O, S, P). The donor is differentiated from the acceptor by that factthat it is less electronegative, or more electropositive, than theacceptor group on the molecule.

The designations Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the substrate.They contain both a PSG unit and an attaching unit.

The PSG unit can be, but is not limited to, any one of following:photosensitive azo, photosensitive ester or ether, photosensitive amideor imide, photosensitive amine or imine, photosensitive carbonate orcarbamate, photosensitive thio-ether or thio-ester, photosensitiveisocyanides, photosensitive hetero-ring system with at least one ofhetero-atom (e.g., N, O, S, B, P etc.).

The attaching unit may be one of the following: carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, hetero atoms (e.g., N, O, S, B, Se, P), or functionalgroups with at least one of above-mentioned hetero atoms, hydrocarbonsor substituted hydrocarbons.

The symbols X₁, X₂, and X₃ represent tuning units built into the ringsystem. The function of these units is to tune the molecule's electronicand/or optical properties as well as to ensure that the ring systemundergoes a smooth and desired tautomerization transition under theinfluence of an applied external E-field. The tuning units may be anyone of the following: hetero atom (e.g., N, P, As, etc.), hydrocarbon,or substituted hydrocarbon.

The symbols G₁ and G₂ are bridging groups. The function of thesebridging groups is to connect the stator and rotor or to connect two ormore fragments to achieve desired molecular properties. They may be anyone of the following: hetero atoms (e.g., N, O, S, P, etc.) orfunctional groups with at least one of above-mentioned hetero atoms(e.g., NH or NHNH, etc.), hydrocarbons (either saturated or unsaturated)or substituted hydrocarbons. The bridging group may alternately comprisea single atom bridge such as an ether bridge with an oxygen atom, or adirect sigma bond between the rotor and stator.

The letter Q is used here to designate a connecting unit between twophenyl rings. It can be any one of following: S, O, NH, NR, hydrocarbon,or substituted hydrocarbon.

The letter H is used here to designate a hydrogen atom.

In Example 1b above, the horizontal dotted lines represent othermolecules or substrates (which can be either an electrode ornon-electrode, depending on the specific application) to which themolecule is optionally linked, or connected. The direction of theswitching field is perpendicular to the horizontal dotted lines.Alternatively, the attaching unit) may be eliminated, and the moleculemay be simply placed between the two electrodes. The molecule shownabove (Example 1b) has been designed with the internal rotor in a 30 to70 degree angle to the orientation axis of the entire molecule. In thiscase, the external field is applied along the orientation axis of themolecule as pictured—the electrodes (horizontal dotted lines) areoriented perpendicular to the plane of the paper and in a 30 to 70degree angle to the orientation axis of the molecule. Application of anelectric field oriented from top to bottom in the diagrams will causethe rotor as pictured in the upper diagram to rotate to the positionshown on the lower diagram, and vice versa. In this case, the rotor aspictured in the lower diagram is not coplanar with the rest of themolecule, so this is the “OFF state” of the molecule, whereas the rotoris essentially coplanar with the rest of the molecule on the upperdiagram, so this is the “ON state” of the molecule.

The molecule depicted in Example 1b in its less conjugated state (“OFF”)is less conductive, and/or chromatically transparent (or blue-shifted inits π-system “localized state”). In its more conjugated state (“ON”),the molecule evidences higher electrical conductivity, and/or color (oris red-shifted).

For the molecules of Example 1b, a single monolayer molecular film isformed, for example, using Langmuir-Blodgett techniques orself-assembled monolayers, such that the orientation axis of themolecules is perpendicular to the plane of the electrodes used to switchthe molecules. Electrodes may be deposited in the manner described byCollier et al, supra, or methods described in the above-referencedpatent applications and patents. Alternate thicker film depositiontechniques include vapor phase deposition, contact or ink-jet printing,spin coating, roll coating and silk screening.

The following requirements must be met in this rotor/stator model:

-   -   (a) The molecule must have at least one rotor and one stator        segment;    -   (b) In one state of the molecule, there should be a delocalized        π-system and/or non-bonding electron(s) that extend over the        large portion of the molecule (rotor(s) and stator(s)), whereas        in the other state, the p-system or π- and non-bonding        electron(s) are localized on the rotor(s) and stator(s);    -   (c) The connecting unit between rotor and stator can be a single        σ-bond or at least one atom with (1) non-bonding electrons (p or        other electrons), or (2) π-electrons, or (3) π-electrons and        non-bonding electron(s) to connect the rotor and stator with the        σ-bond;    -   (d) The non-bonding electrons, or π-electrons, or π-electrons        and non-bonding electron(s) of the rotor(s) and stator(s) can be        localized or delocalized depending on the conformation of the        molecule while the rotor rotates when activated by an E-field;    -   (e) The conformation(s) of the molecule can be E-field dependent        or bistable;    -   (f) The bistable state(s) can be achieved by intra- or        intermolecular forces such as hydrogen bonding, Coulomb force,        van der Waals force, metal ion complex or dipole        inter-stabilization; and    -   (g) The band gap of the molecule will change depending on the        degree of non-bonding electron, or π-electron, or π-electron and        non-bonding electron de-localization of the molecule. This will        change the conductivity of the molecule.

Example 1c below shows a real molecular example of another embodiment ofthe present invention. In Example 1c, the device contains twophotosensitive connecting groups. Upon irradiation, e.g., UV, theconnecting groups decompose to form thiol and 2-nitrophenylacetic acid,which is removable by washing with a base.

where:

The symbol A⁻ is an Acceptor group; it is an electron-withdrawing group.It may be one of following: carboxylic acid or its derivatives, sulfuricacid or its derivatives, phosphoric acid or its derivatives, nitro,nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br), functional groupwith at least one of above-mentioned hetero atoms (e.g., OH, SH, NH,etc.), hydrocarbons (either saturated or unsaturated), or substitutedhydrocarbons.

The symbol D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), substituted hydrocarbon,or a functional group with at least one hetero atom (e.g., B, Si, I, N,O, S, P). The donor is differentiated from the acceptor by that factthat it is less electronegative, or more electropositive, than theacceptor group on the molecule.

The designation Con₂ represents optional connecting units between onemolecule and another molecule or between a molecule and the substrate.They contain both a PSG unit and an attaching unit. Alternatively, theattaching unit may be eliminated, and the molecule may be simply placedbetween the two electrodes.

Symbols X₁, X₂, and X₃ represent tuning units built into the ringsystem. The function of these units is to tune the molecule's electronicand/or optical properties as well as to ensure that the ring systemundergoes a smooth and desired tautomerization transition under theinfluence of an applied external E-field. They may be any one of thefollowing: hetero atom (e.g., N, P, As, etc.), hydrocarbons, orsubstituted hydrocarbons.

Symbols G₁ and G₂ are bridging groups. The function of these bridginggroups is to connect the stator and rotor or to connect two or morefragments to achieve desired molecular properties. They may be any oneof the following: hetero atoms (e.g., N, O, S, P, etc.) or functionalgroups with at least one of above-mentioned hetero atoms (e.g., NH orNHNH, etc.), hydrocarbons (either saturated or unsaturated) orsubstituted hydrocarbons. The bridging group may alternately comprise asingle atom bridge such as an ether bridge with an oxygen atom, or adirect sigma bond between the rotor and stator.

The letter Q is used here to designate a connecting unit between twophenyl rings. It can be any one of following: S, O, NH, NR, hydrocarbon,or substituted hydrocarbon.

The letter H is used here to designate a hydrogen atom.

Turning now to Example 2a, this depicts a second embodiment of thePSG-modified bistable molecular mechanical device of the presentinvention.

where:

The symbol A⁻ is an Acceptor group; it is an electron-withdrawing group.It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid and itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),or a functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), or hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

The symbol D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), substituted hydrocarbon,or a functional group with at least one hetero atom (e.g., B, Si, I, N,O, S, P). The donor is differentiated from the acceptor by that factthat it is less electronegative, or more electropositive, than theacceptor group on the molecule.

The items; G₁═G₂, G₃═G₄, G₅═G₆, and G₇═G₈ are bridging groups. Thefunction of these bridging groups is to connect the stator and rotor orto connect two or more conjugated rings to achieve a desired electronicproperty. They may be a PSG unit or not. They may be double bondedgroups with any one or a combination of the following: hetero atoms(e.g., C, N, O, S, P, etc.) or a functional group with at least one ofthe above-mentioned hetero atoms (e.g., NH or NHNH, etc.), hydrocarbons(either saturated or unsaturated) or substituted hydrocarbons. Thebridging group may alternately comprise a single atom bridge such as anether bridge with an oxygen atom, or a direct sigma bond between therotor and stator.

The designations Con₁ and Con₂ represent optional connecting unitsbetween one molecule and another molecule or between a molecule and thesubstrate. They contain both a PSG unit and an attaching unit.Alternatively, the attaching unit may be eliminated, and the moleculemay be simply placed between the two electrodes. The PSG unit can be,but is not limited to, any one of following: photosensitive azo,photosensitive ester or ether, photosensitive amide or imide,photosensitive amine or imine, photosensitive carbonate or carbamate,photosensitive thio-ether or thio-ester, photosensitive isocyanides, orphotosensitive hetero-ring system with at least one hetero-atom (e.g.,N, O, S, B, P etc.).

The attaching unit may be one of the following: carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, hetero atoms (e.g., N, O, S, B, Se, P), or functionalgroups with at least one of above-mentioned hetero atoms, hydrocarbons,or substituted hydrocarbons

The symbols R₁, R₂, and R₃ represent spacing groups built into themolecule. The function of these spacer units is to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor. They may beany one of the following: hydrogen, hydrocarbon (either saturated orunsaturated), or substituted hydrocarbon.

The symbols J₁ and J₂ represent tuning groups built into the molecule.The function of these tuning groups (e.g., OH, NHR, COOH, CN, nitro,etc.) is to provide an appropriate functional effect (e.g. bothinductive effect and resonance effects) and/or steric effect(s). Thefunctional effect is to tune the band gap (ΔE_(HOMO/LUMO)) of themolecule to obtain the desired electronic properties of the molecule(ΔE_(HOMO/LUMO)=0.5 to 2.5 eV). The steric effect is to tune themolecular conformation through steric hindrance, inter- orintra-molecular interaction forces (e.g., hydrogen bonding, Coulombinteraction, van der Waals forces) or to provide bi- ormultiple-stability of molecular orientations. They may be any one of thefollowing: hydrogen, hetero atoms (e.g., N, O, S, P, B, F, Cl, Br, andI), functional groups with at least one of above-mentioned hetero atoms,or hydrocarbons (either saturated or unsaturated).

When the double-bonded groups G₁═G₂, G₃═G₄, G₅═G₆, and G₇═G₈ arephotosensitive bridging groups, they can undergo photochemicaldecomposition upon irradiation to break the main body of the molecularswitching system into several small pieces, and consequently, themolecular system will be removed easily from the substrate by a simplesolvent extraction or washing.

Example 2b below shows a real example of a PSG-modified switchablemolecule, which contains PSGs on both the connecting units and thebridging groups Upon UV irradiation, both connecting groups and bridginggroups decompose to form small molecules, which are removable by baseand/or solvent washing.

where:

The symbol A⁻ is an Acceptor group; it is an electron-withdrawing group.It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid and itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),or a functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), hydrocarbon (either saturated or unsaturated),or substituted hydrocarbon.

The symbol D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), substituted hydrocarbon,or a functional group with at least one hetero atom (e.g., B, Si, I, N,O, S, P). The donor is differentiated from the acceptor by that factthat it is less electronegative, or more electropositive, than theacceptor group on the molecule.

The symbols R₁, R₂, and R₃ represent spacing groups built into themolecule. The function of these spacer units is to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor. They may beany one of the following: hydrogen, hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

The symbols J₁ and J₂ represent tuning groups built into the molecule.The function of these tuning groups (e.g., OH, NHR, COOH, CN, nitro,etc.) is to provide an appropriate functional effect (e.g. bothinductive effect and resonance effects) and/or steric effects. Thefunctional effect is to tune the band gap (ΔE_(HOMO/LUMO)) of themolecule to obtain the desired electronic properties of the molecule.The steric effect is to tune the molecular conformation through sterichindrance, inter- or intra-molecular interaction forces (e.g. hydrogenbonding, Coulomb interaction, van der Waals forces) or to provide bi- ormultiple-stability of molecular orientations. They may be any one of thefollowing: hydrogen, hetero atoms (e.g., N, O, S, P, B, F, Cl, Br, andI), functional groups with at least one of above-mentioned hetero atoms,hydrocarbons (either saturated or unsaturated).

Turning now to Example 3, this depicts a third embodiment of the PSGmodified bistable molecular mechanical device of the present invention.Example 3a, shown in FIG. 7, depicts another generic molecular examplefor the present invention. In this example, the main molecular switchingunit 62′, which is bonded to one or more solvent-insoluble PSGs 66′ toform molecule 70′, cannot be physically removed via extraction orwashing. However, exposure to electromagnetic radiation Hν causes aphotochemical transformation that converts the solvent-insoluble PSGs66′ into solvent-soluble functional groups 72, and the main molecularswitching unit 62′ can now be easily removed via extraction or washing.

Example 3b depicts a specific molecular system:

where:

The symbol A⁻ is an Acceptor group; it is an electron-withdrawing group.It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid and itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),a functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), hydrocarbon (either saturated or unsaturated),or substituted hydrocarbon.

The symbol D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), substituted hydrocarbon,or functional group with at least one hetero atom (e.g., B, Si, I, N, O,S, P). The donor is differentiated from the acceptor by that fact thatit is less electronegative, or more electropositive, than the acceptorgroup on the molecule.

The items labeled G₁═G₂, G₃═G₄, G₅═G₆, and G₇═G₈ are bridging groups.The function of these bridging groups is to connect the stator and rotoror to connect two or more conjugated rings to achieve a desiredelectronic property. They may be PSG units or not. They may bedouble-bonded groups with any one or a combination of the following:hetero atoms (e.g., C, N, O, S, P, etc.) or a functional group with atleast one of the above-mentioned hetero atoms (e.g., NH or NHNH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons. The bridging group may alternately comprise a single atombridge such as an ether bridge with an oxygen atom, or a direct sigmabond between the rotor and stator.

The designations Con₁ and Con₂ represent optional connecting unitsbetween one molecule and another molecule or between a molecule and thesubstrate. They contain both a PSG unit and an attaching unit.Alternatively, the attaching unit may be eliminated, and the moleculemay be simply placed between the two electrodes.

The symbols J₁, J₂, J₃, and J₄ represent tuning groups built into themolecule, which contains water-soluble and/or solvent-soluble functionalgroups (e.g., OH, NHR, COOH, CN, etc.). The designations J₁-PSG, J₂-PSG,J₃-PSG, and J₄-PSG represent the linkage of the tuning groups with PSGs,which could be ether, ester, carbonate, or carbonate linkages. Uponirradiation, e.g., UV, these linkages decompose to liberatewater-soluble and/or solvent-soluble tuning groups, which are removableby water and/or solvent.

The PSG unit can be, but is not limited to, any one of following:photosensitive azo, photosensitive ester or ether, photosensitive amideor imide, photosensitive amine or imine, photosensitive carbonate orcarbamate, photosensitive thioether or thio-ester, photosensitiveisocyanides, photosensitive hetero-ring system with at least onehetero-atom (e.g. N, O, S, B, P etc.).

The attaching unit may be one of the following: carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, hetero atoms (e.g., N, O, S, B, Se, P), or functionalgroups with at least one of above-mentioned hetero atoms, hydrocarbonsor substituted hydrocarbons.

The commonly-known PSGs are listed in Table I below:

TABLE I Photosensitive Groups and UV Wavelength of Sensitivity.Photosensitive Group UV Wavelength α-carboxy-2-nitrobenzyl (CNB) 260 nm1-(2-nitrophenyl)ethyl (NPE) 260 nm 4,5-dimethoxy-2-nitrobenzyl (DMNB)355 nm 1-(4,5-dimethoxy-2-nitrophenyl)ethyl (DMNPE) 355 nm(4,5-dimethoxy-2-nitrobenzyloxy)carbonyl (NVOC) 355 nm5-carboxymethoxy-2-nitrobenzyl (CMNB) 320 nm[(5-carboxymethoxy-2-nitrobenzyl)oxy]carbonyl 320 nm (CMNCBZ)desoxybenzoinyl (desyl) 360 nm anthraquinon-2-ylmethoxycarbonyl (AQMOC)350 nm

Any of the preceding PSGs may be employed in any of the precedingexamples.

In the above examples, the method of patterning the film throughphotonic molecular change is accomplished by a destructive effect, whichis similar to the manner in which positive photoresist acts (i.e.,irradiated photoresist undergoes a chemical change to break bonds andallow its removal in an appropriate solvent, whereas the unirradiatedareas are substantially unaffected by that same solvent).

Additionally, there is another manner by which molecular photopatterningcould occur through irradiation, namely, a constructive change (seeExamples 4a and 4b, below). In constructive change, a molecule withappropriate photosensitive links would be altered by irradiation so thatmolecules in the areas irradiated would not be removed from thesubstrate by the same solvent/base as the unexposed molecular region.The change could be an alteration of structural molecular form or theremoval of specific sensitive groups after the breaking of a bond orbonds by irradiation.

Turning now to Example 4, this example depicts a fourth embodiment ofthe PSG modified bistable molecular mechanical device of the presentinvention. Example 4a depicts another generic molecular example for thepresent invention. This case is essentially the reverse of that depictedin FIG. 7. Here, the main molecular switching unit 62′ has bondedthereto one or more solvent-soluble PSGs 66″ to form molecule 70″, whichmay be soluble in one or more solvents. In this case, the untransformedmolecule 70″ is soluble in at least one solvent, and can be physicallyremoved via extraction or washing. However, exposure to electromagneticradiation hν causes a photochemical transformation that converts thesolvent-soluble PSGs 66″ into solvent-insoluble functional groups 74,and the main molecular switching unit 62′ is no longer soluble in any ofthe previously-used solvents, and can no longer be easily removed viaextraction or washing.

Example 4b shows a real example of a PSG-modified switchable molecule,which contains PSGs on the side-arms of the molecular device. Due to thecarboxylic acid groups of the PSGs on the molecule, the molecule issoluble in aqueous base(s) or solvent(s). Upon irradiation, e.g., UV,the acid groups have been transformed into —SH groups, which results ina change in the solubility of the molecule in certain solvent(s), Thetransformed molecule is no longer soluble in basic water or basicsolvent(s). One can use this type of molecule to directly pattern thedevice via the photo-patterning method of the present invention, andthen wash or extract off those photochemically-untransformed moleculesto obtain the desired molecular circuits.

INDUSTRIAL APPLICABILITY

The use of a molecular photoresist as described herein is expected tofind use in the fabrication of micrometer-scale and nanometer-scaledevices.

1. A bistable molecule for a multiple electrode device, said multipleelectrode device comprising at least one pair of electrodes that form atleast one junction and at least one said bistable molecule connectingsaid pair of electrodes in said junction, said junction having afunctional dimension in nanometers or micrometers, said bistablemolecule including at least one photosensitive, photodecomposablefunctional group, wherein said bistable molecule comprises a main chainand at least one pendant group and wherein at least one photosensitive,photodecomposable functional group is attached either to said main chainor to said pendant group, said bistable molecule exhibiting bistabilityirrespective of the presence or absence of said at least onephotosensitive, photodecomposable group.
 2. The bistable molecule ofclaim 1 wherein said photosensitive functional group is sensitive toultraviolet, electron-beam, or X-ray radiation.
 3. The bistable moleculeof claim 1 wherein one said photosensitive group is attached to at leastone end of said bistable molecule.
 4. The bistable molecule of claim 1wherein said photosensitive group is selected from the group consistingof α-carboxy-2-nitrobenzyl; 1-(2-nitrophenyl)ethyl;4,5-dimethoxy-2-nitrobenzyl; 1-(4,5-dimethoxy-2-nitrophenyl)ethyl;(4,5-dimethoxy-2-nitrobenzyloxy)carbonyl;5-carboxymethoxy-2-nitrobenzyl;[(5-carboxymethoxy-2-nitrobenzyl)oxy]carbonyl; desoxybenzoinyl; andanthraquinon-2-ylmethoxycarbonyl.
 5. The bistable molecule of claim 1wherein said molecule evidences switching based on electric (E) fieldinduced band gap change, selected from the group consisting of: (1) anelectric field (“E-field”) induced rotation of at least one rotatablesection (rotor) of a molecule to change the band gap of the molecule(rotor/stator configuration); (2) E-field-induced charge separation orrecombination of the molecule via chemical bonding change to alter theband gap: (2a) E-field-induced band gap change caused by the change ofextended conjugation via charge separation or recombination accompaniedby increasing or decreasing π- and/or p-electron localization; (2b)E-field-induced band gap change caused by a change of extendedconjugation via charge separation or recombination and π-bond breakingor formation; and (3) E-field-induced band gap change via molecularfolding or stretching.
 6. The bistable molecule of claim 5 wherein saidbistable molecule comprises:

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of (a) carboxylic acid and itsderivatives, (b) sulfuric acid and its derivatives, (c) phosphoric acidand its derivatives, (d) nitro, (e) nitrile, (f) hetero atoms selectedfrom the group consisting of N, O, S, P, F, Cl, and Br, (g) functionalgroups with at least one of said hetero atoms, (h) saturated orunsaturated hydrocarbons, and (i) substituted hydrocarbons; D⁺ is aDonor group comprising an electron-donating group selected from thegroup consisting of (a) hydrogen, (b) amines, (c) OH, (d) SH; (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinsaid Donor group is more electropositive than said Acceptor group; Con₁and Con₂ are connecting units between one molecule and another moleculeor between a molecule and a substrate, said connecting units containingan attaching unit and at least one of said connecting units containingsaid photosensitive group, wherein said photosensitive group is selectedfrom the group consisting of photosensitive azo, photosensitive ester,photosensitive ether, photosensitive amide, photosensitive imide,photosensitive amine, photosensitive imine, photosensitive carbonate,photosensitive carbamate, photosensitive thio-ether, photosensitivethio-ester, photosensitive isocyanides, and photosensitive hetero-ringsystems with at least one hetero-atom selected from the group consistingof N, O, S, B, and P, and wherein the attaching unit is selected fromthe group consisting of (a) carboxylic acid and its derivatives, (b)sulfuric acid and its derivatives, (c) phosphoric acid and itsderivatives, (d) hetero atoms selected from the group consisting of N,O, S, B, Se, and P, (e) functional groups with at least one of saidhetero atoms (f) hydrocarbons, and (g) substituted hydrocarbons; X₁, X₂,X₃ are tuning units built into the ring system which serve to tune theelectronic properties, the optical properties, or both, of the bistablemolecule as well those of the ring system undergo a smooth and desiredtautomerization transition under the influence of an applied externalE-field, wherein the tuning units are selected from the group consistingof a hetero atom selected from the group consisting of N, P, and As;hydrocarbons; and substituted hydrocarbons; G₁ and G₂ are bridginggroups for connecting stator and rotor portions of said bistablemolecule or for connecting two or more fragments to achieve desiredmolecular properties, wherein the bridging groups are either (a)selected from the group consisting of (i) hetero atoms selected from thegroup consisting of N, O, S, and P; (ii) functional groups with at leastone of said hetero atoms; (iii) saturated or unsaturated hydrocarbons;and (iv) substituted hydrocarbons or (b) selected from the groupconsisting of a single atom bridge and a direct sigma bond between saidrotor and stator portions; Q is a connecting unit between two phenylrings, selected from the group consisting of S, O, NH, NR, hydrocarbons,and substituted hydrocarbons; and H is a hydrogen atom.
 7. The bistablemolecule of claim 5 wherein said bistable molecule comprises:

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of (a) carboxylic acid and itsderivatives, (b) sulfuric acid and its derivatives, (c) phosphoric acidand its derivatives, (d) nitro, (e) nitrile, (f) hetero atoms selectedfrom the group consisting of N, O, S, P, F, Cl, and Br, (g) functionalgroups with at least one of said hetero atoms, (h) saturated orunsaturated hydrocarbons, and (i) substituted hydrocarbons; D⁺ is aDonor group comprising an electron-donating group selected from thegroup consisting of (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P, whereinsaid Donor group is more electropositive than said Acceptor group; Con₂is a connecting unit between one molecule and another molecule orbetween a molecule and a substrate, said connecting unit containing anattaching unit and said photosensitive group, wherein saidphotosensitive group is selected from the group consisting ofphotosensitive azo, photosensitive ester, photosensitive ether,photosensitive amide, photosensitive imide, photosensitive amine,photosensitive imide, photosensitive carbonate, photosensitivecarbamate, photosensitive thio-ether, photosensitive thio-ester,photosensitive isocyanides, and photosensitive hetero-ring systems withat least one hetero-atom selected from the group consisting of N, O, S,B, and P and wherein the attaching unit is selected from the groupconsisting of carboxylic acid and its derivatives; sulfuric acid and itsderivatives; phosphoric acid and its derivatives; hetero atoms selectedfrom the group consisting of N, O, S, B, Se, and P functional groupswith at least one of said hetero atoms; hydrocarbons; and substitutedhydrocarbons; X₁, X₂, X₃ are tuning units built into the ring systemwhich serve to tune the electronic properties, the optical properties,or both, of the bistable molecule as well as to that the ring systemundergoes a smooth and desired tautomerization transition under theinfluence of an applied external E-field, wherein the tuning units areselected from the group consisting of a hetero atom selected from thegroup consisting of N, P, and As; hydrocarbons; and substitutedhydrocarbons; G₁ and G₂ are bridging groups for connecting stator androtor portions of said bistable molecule or for connecting two or morefragments to achieve desired molecular properties, wherein the bridginggroups are either (a) selected from the group consisting of (i) heteroatoms selected from the group consisting of N, O, S, and P; (ii)functional groups with at least one of said hetero atoms; (iii)saturated or unsaturated hydrocarbons; and (iv) substituted hydrocarbonsor (b) selected from the group consisting of a single atom bridge and adirect sigma bond between said rotor and stator portions; Q is aconnecting unit between two phenyl rings, selected from the groupconsisting of S, O, NH, NR, hydrocarbons, and substituted hydrocarbons;and H is a hydrogen atom.
 8. The bistable molecule of claim 5 whereinsaid bistable molecule comprises:

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of (a) carboxylic acid and itsderivatives, (b) sulfuric acid and its derivatives, (c) phosphoric acidand its derivatives, (d) nitro, (e) nitrile, (f) hetero atoms selectedfrom the group consisting of N, O, S, P, F, Cl, and Br, (g) functionalgroups with at least one of said hetero atoms, (h) saturated orunsaturated hydrocarbons, and (i) substituted hydrocarbons; D⁺ is aDonor group comprising an electron-donating group selected from thegroup consisting of (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P; whereinsaid Donor group is more electropositive than said Acceptor group; G₁ 50G₂, G₃═G₄, G₅═G₆, and G₇═G₈ are bridging groups for connecting statorand rotor portions of said bistable molecule or for connecting two ormore conjugated rings to achieve desired electronic properties, whereinthe bridging groups are either (a) photosensitive functional groups or(b) selected from the group consisting of (i) hetero atoms selected fromthe group consisting of N, O, S, and P; (ii) functional groups with atleast one of said hetero atoms; (iii) saturated or unsaturatedhydrocarbons; and (iv) substituted hydrocarbons, or (c) selected fromthe group consisting of a single atom bridge and a direct sigma bondbetween said rotor and stator portions; Con₁ and Con₂ are connectingunits between one molecule and another molecule or between a moleculeand a substrate, said connecting units containing an attaching unit andat least one of said connecting units containing said photosensitivegroup, wherein said photosensitive group is selected from the groupconsisting of photosensitive azo, photosensitive ester, photosensitiveether, photosensitive amide, photosensitive imide, photosensitive amine,photosensitive imine, photosensitive carbonate, photosensitivecarbamate, photosensitive thio-ether, photosensitive thio-ester,photosensitive isocyanides, and photosensitive hetero-ring systems withat least one hetero-atom selected from the group consisting of N, O, S,B, and P and wherein the attaching unit is selected from the groupconsisting of carboxylic acid and its derivatives; sulfuric acid and itsderivatives; phosphoric acid and its derivatives; hetero atoms selectedfrom the group consisting of N, O, S, B, Se, and P; functional groupswith at least one of said hetero atoms; hydrocarbons, and substitutedhydrocarbons; R₁, R₂, and R₃ are spacing groups selected from the groupconsisting of(a) hydrogen, (b) saturated or unsaturated hydrocarbons,and (c) substituted hydrocarbons; and J₁ and J₂ are tuning groups toprovide at least one appropriate functional effect selected from thegroup consisting of inductive effects, resonance effects, and stericeffects, where said tuning groups are selected from the group consistingof (a) hydrogen, (b) hetero atoms selected from the group consisting ofN, O, S, P, B, F, Cl, Br, and I, (c) functional groups with at least oneof said hetero atoms, (d) saturated or unsaturated hydrocarbons, and (e)substituted hydrocarbons.
 9. The bistable molecule of claim 5 whereinsaid bistable molecule comprises:

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of (a) carboxylic acid and itsderivatives, (b) sulfuric acid and its derivatives, (c) phosphoric acidand its derivatives, (d) nitro, (e) nitrile, (f) hetero atoms selectedfrom the group consisting of N, O, S, P, F, Cl, and Br, (g) functionalgroups with at least one of said hetero atoms, (h) saturated orunsaturated hydrocarbons, and (i) substituted hydrocarbons; D⁺ is aDonor group comprising an electron-donating group selected from thegroup consisting of (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P; whereinsaid Donor group is more electropositive than said Acceptor group; R₁,R₂, and R₃ are spacing groups selected from the group consisting of (a)hydrogen, (b) saturated or unsaturated hydrocarbons, and (c) substitutedhydrocarbons; and J₁ and J₂ are tuning groups to provide at least oneappropriate functional effect selected from the group consisting ofinductive effects, resonance effects, and steric effects, said tuninggroups are selected from the group consisting of (a) hydrogen, (b)hetero atoms selected from the group consisting of N, O, S, P, B, F, Cl,Br, and I, (c) functional groups with at least one of said hetero atoms,(d) saturated or unsaturated hydrocarbons, and (e) substitutedhydrocarbons.
 10. The bistable molecule of claim 5 wherein said bistablemolecule comprises:

where: A⁻ is an Acceptor group comprising an electron-withdrawing groupselected from the group consisting of (a) carboxylic acid and itsderivatives, (b) sulfuric acid and its derivatives, (c) phosphoric acidand its derivatives, (d) nitro, (e) nitrile, (f) hetero atoms selectedfrom the group consisting of N, O, S, P, F, Cl, and Br, (g) functionalgroups with at least one of said hetero atoms, (h) saturated orunsaturated hydrocarbons, and (i) substituted hydrocarbons; D⁺ is aDonor group comprising an electron-donating group selected from thegroup consisting of (a) hydrogen, (b) amines, (c) OH, (d) SH, (e)ethers, (f) saturated or unsaturated hydrocarbons, (g) substitutedhydrocarbons, and (h) functional groups with at least one hetero atomselected from the group consisting of B, Si, I, N, O, S, and P; whereinsaid Donor group is more electropositive than said Acceptor group;G₁═G₂, G₃═G₄, G₅═G₆, and G₇═G₈ are bridging groups for connecting statorand rotor portions of said bistable molecule or for connecting two ormore conjugated rings to achieve desired electronic properties, whereinthe bridging groups are either (a) photosensitive functional groups, or(b) selected from the group consisting of (i) hetero atoms selected fromthe group consisting of N, O, S, and P; (ii) functional groups with atleast one of said hetero atoms; (iii) saturated or unsaturatedhydrocarbons; and (iv) substituted hydrocarbons, or (c) selected fromthe group consisting of a single atom bridge and a direct sigma bondbetween said rotor and stator portions; Con₁ and Con₂ are connectingunits between one molecule and another molecule or between a moleculeand a substrate, said connecting units containing an attaching unit andat least one of said connecting units containing said photosensitivegroup, wherein said photosensitive group is selected from the groupconsisting of photosensitive azo, photosensitive ester, photosensitiveether, photosensitive amide, photosensitive imide, photosensitive amine,photosensitive imine, photosensitive carbonate, photosensitivecarbamate, photosensitive thio-ether, photosensitive thio-ester,photosensitive isocyanides, and photosensitive hetero-ring systems withat least one hetero-atom selected from the group consisting of N, O, S,B, and P and wherein the attaching unit is selected from the groupconsisting of carboxylic acid and its derivatives; sulfuric acid and itsderivatives; phosphoric acid and its derivatives; hetero atoms selectedfrom the group consisting of N, O, S, B, Se, and P; functional groupswith at least one of said hetero atoms; hydrocarbons; and substitutedhydrocarbons; and J₁, J₂, J₃, and J₄ are tuning groups which containsolvent functional groups selected from the group consisting of OH, NHR,COOH, and CN, where R is alkyl or aryl, wherein J₁-PSG, J₂-PSG, J₃-PSG,and J₄-PSG are linkages of said tuning groups with said photosensitivegroups and are selected from the group consisting of ether, ester,carbonate, amide, and carbamate linkages.